Mailbox flag holder



FIG. 1 is a perspective view of a mailbox flag holder, showing my new design mounted on a mailbox shown in broken lines;

FIG. 2 is a perspective view thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a front elevational view thereof, the rear elevational view being a mirror image; and,

FIG. 5 is a top plan view thereof.

The bottom forms no part of the claimed design.

The broken lines form no part of the claimed design.

All surfaces not shown form no part of the claimed design. 

CLAIM The ornamental design for a mailbox flag holder, as shown and described. 